1. Technical Field
The present application relates to tools for the machining of materials by milling.
2. Background Information
Background information is for informational purposes only and does not necessarily admit that subsequently mentioned information and publications are prior art.
Milling cutters are widely used in milling operations due to their versatile range of application and due to the moderate first cost of the tool. Milling cutters are often of cylindrical shape, and are available up to about eighty millimeter diameter, although the present application refers to the diameter range of about five millimeters to about thirty-two millimeters. Many milling cutters have flat ends; however, other shapes such as conical and rounded ends are also used. A milling cutter typically has two to ten teeth, depending on diameter size and whether for rough cutting or finishing. Teeth are usually of spiral shape, but can be straight parallel or virtually parallel to the axis. Material of construction is high speed steel, solid carbide, Cubic boron nitride, Poly crystal diamond, cermet, ceramic, and combinations thereof.
Some cutting tools include an insert having a plurality of cutting edges of inwardly directed V shaped geometry. The insert has inner and outer flank cutting edges with rounded corners. The cutting edge is divided by a chisel edge into roughing and finishing cutting portions.
Two known problems with regard to screw-on inserts are that high precision in positioning the insert is desired to restrict or minimize making over-size holes, and the screw holding the insert has a tendency to loosen due to vibration of the tool when in use. Yet a further problem regarding tools using two inserts is that high precision is indispensable in the settings of the two inserts which should be identical. Due to the size of the insert which should be large enough to allow setting and clamping, small and medium size holes can not be machined.
On side surfaces of similar inserts, a clearance surface formed on a protruding portion which, via a step clearance extends into a secondary helically twisted clearance surface, the chip angle of which increases with increasing cutting depth. The insert includes a chip breaker.
Some milling cutters have at least one flute with a low angle cutting surface while a second flute has a high angle cutting surface. The two flutes intersect to form a compound cutting surface.
Some milling cutters have flat bottoms and rounded corners. The corner configuration described improves resistance to chipping and fracture of the milling cutter.
Some milling cutters have an about thirty-five degree helix angle to about sixty degree helix angle and a core diameter about sixty-two percent to about sixty-eight percent of the outer diameter. Cutting edges are ultra-fine cemented carbide. These milling cutters improve chip discharge and reduce corner wear.
Some milling cutters have a highly smooth and polished cutting edge land bordering the cutting edge. The obvious problem here is that the polished area will not survive for more than a few minutes of work.
Some milling cutters of defined form are intended for executing rough machining and finish machining.
A large number of tooth forms for end mills and milling cutters are known. In order to decide which form is best, it would be desirable to run comparative and extensive machining tests on cutters made according to the various disclosures in the literature. Such tests have rarely been carried out due to the high expense involved. Presently, most inventors test run the form of their choice in a workshop, but even where machining test results are published, conditions of machining (material hardness, cutter diameter and material, number of teeth, machine rigidity, machining speed and feed, coolant composition, surface finish quality, whether the milling cutter is nitride coated or not, and yet further factors) are not standardized and can not be compared. In the absence of comparative test results it is difficult to assess the merits of prior-art disclosures regarding tooth shapes.
The face milling cutter according to the present specification has however been extensively tested and has been found to have improved machining results when used on practical work pieces, in comparison with other milling cutters which were tested on the same machining task. The present inventors (referred to in the test report by the name “HANITA”) have carried out testing using milling cutters with twelve millimeter diameters with the primary criterion being wear on the maximum diameter of the tool while machining recesses in 4340 alloy steel.
Many prior-art milling cutters operate quite satisfactorily on non-ferrous metals and on soft steel. However, for cutting tool steel, a frequent requirement in the manufacture of dies, punches, casting dies, forging dies and press tools, feed rates drop sharply, vibrations are generated and tool breakage occurs.